The conventional combine harvester after separation of straw and chaff from the materials to be collected, discharges the straw and chaff from a rear discharge area of the combine harvester. The straw is generally discharged at the rearmost part of the housing in a generally downward direction from the straw walkers or other separation system.
The chaff is generally discharged at a position just in front of the straw discharge point from the rear end of the chaffer sieve.
In many cases the combine includes a chopper assembly mounted on the combine harvester body at a position just downward of the straw discharge point for applying a chopping action to the straw. Generally the straw chopper comprises a horizontal hub member mounted across the rear of the combine harvester body with a plurality of chopper blades or flails mounted on the hub member for rotation about the axis of the hub member. The straw is simply fed downwardly onto the chopper at a position forwardly of the axis, is grasped by the blade members and carried thereby past a plurality of stationary blades which apply a chopping or cutting action to the straw that is carried. The straw after chopping is then simply thrown from the flails rearwardly of the combine. Some attempts have been made to spread the straw by providing fins which curve rearwardly and then outwardly to the sides to deflect the straw as it is thrown across the width wider than that of the combine harvester itself.
Such choppers are however ineffective in many ways. Most importantly there is little spreading action of the straw due to the fact that the air surrounding the straw is basically stationary. Thus the straw is simply thrown into the air rather than as part of a stream of air thus causing the straw to rapidly loose velocity and drop to the ground.
In addition the chopping action is somewhat limited and can fail on tougher materials causing the unchopped materials to wrap around the chopper assembly thus rapidly causing a blockage.
The blades of the chopping assembly simply comprise a flat blade lying in a radial plane of the chopper axis with the blades passing between stationary blades surfaces also lying in a radial plane but offset from the rotating blades of the chopper assembly.
Some attempts have been made to improve the chopping action simply by decreasing the spacing between the rotating blades and the stationary blades but this has had no effect on the ability of the chopping assembly to propel the chopped materials.
Furthermore, if the chopping assembly were fed with chaff from the chaff discharge opening of the combine harvester this would have little or no effect on the chaff so the chaff is generally discharged simply rearwardly of the combine harvester.
Attempts have been made to increase the spreading action of both the chaff and the straw by providing fans which generate an air stream sucking air and the material into the centre of the fan in a direction longitudinal of the axis of the fan and then propelling the material and the air stream radially outwardly from the fan. In this case the fan is generally mounted with the axis vertical so the blades lie in a horizontal plane. One example of a device of this type is shown in U.S. Pat. No. 4,235,716 (Scott et al) and is known in practice as "Straw Storm" (TM). A further example is shown in U.S. Pat. No. 4,292,795 (Linn). A device designed for spreading chaff separately from the straw is shown in U.S. Pat. No. 4,591,102 (Clarke) and is known as "Hurricane" (TM) chaff spreader.
These devices have achieved some success but are relatively expensive, complex and require the use of gear boxes which are of course always prone to failure.